An approach to the use of packaged statistical programs for cluster,classification, and discriminant analysis of trace element data     

Vanda Vitali  Ursula M. Franklin 《Geoarchaeology》1986,1(2):195-201

The purpose of this paper is to present an approach to be taken when using packaged statistical programs for the evaluation of multivariate data, in particular those programs designed for clustering, classification, and discrimination purposes. A systematic step-by-step approach is outlined starting with those steps which should be conducted in order to assure that the assumptions underlying the statistical analyses are satisfied. The use of various methods and computational options in cluster, classification, and discriminant analysis is then discussed. Finally the need for an assessment of the results in view of the overall knowledge of the problem is pointed out.  相似文献   

Placing the Deep Impact Mission into context: Two decades of observations of 9P/Tempel 1 from McDonald Observatory     

A.L. Cochran  E.S. Barker  J. Györgey-Ries 《Icarus》2009,199(1):119-128

We report on low-spectral resolution observations of Comet 9P/Tempel 1 from 1983, 1989, 1994 and 2005 using the 2.7 m Harlan J. Smith telescope of McDonald Observatory. This comet was the target of NASA's Deep Impact mission and our observations allowed us to characterize the comet prior to the impact. We found that the comet showed a decrease in gas production from 1983 to 2005, with the decrease being different factors for different species. OH decreased by a factor 2.7, NH by 1.7, CN by 1.6, C₃ by 1.8, CH by 1.4 and C₂ by 1.3. Despite the decrease in overall gas production and these slightly different decrease factors, we find that the gas production rates of OH, NH, C₃, CH and C₂ ratioed to that of CN were constant over all of the apparitions. We saw no change in the production rate ratios after the impact. We found that the peak gas production occurred about two months prior to perihelion. Comet Tempel 1 is a “normal” comet.  相似文献   

Temporal Trends of Dissolved Trace Metals in Jamaica Bay,NY: Importance of Wastewater Input and Submarine Groundwater Discharge in an Urban Estuary   总被引：1，自引：0，他引：1  

Aaron J. Beck  J. Kirk Cochran  Sergio A. Sañudo-Wilhelmy 《Estuaries and Coasts》2009,32(3):535-550

Jamaica Bay, NY, is a highly urbanized estuary within the boroughs of New York City conspicuously lacking published information on dissolved trace metal concentrations. The current study examines the distribution and cycling of trace metals in that embayment with data gathered during cruises in November 2004, April 2005, and June 2006. Most of the metal distributions (Fe, Zn, Co, Ag, Cu, Pb, Ni) in the water column are explained by the input of substantial volumes of treated wastewater effluent. However, several lines of evidence suggest that submarine groundwater discharge (SGD) is also an important source of dissolved Fe, Zn, Co, Ni, and isotopically distinct stable Pb ratios (²⁰⁶Pb, ²⁰⁷Pb, ²⁰⁸Pb) in the Bay. Conversely, the recirculated seawater component of SGD is an apparent sink for dissolved Mo. This study provides the first measurements of dissolved trace metals in the Jamaica Bay water column and subterranean estuary and provides evidence for trace metal input due to SGD.  相似文献   

Paleoecology of mangroves along the Sibun River, Belize     

Natalie M. Monacci  Ursula Meier-Grünhagen  Bruce P. Finney  Hermann Behling  Matthew J. Wooller 《Quaternary Research》2011,76(2):220-228

This study examines a sediment core (SR-63) from a mangrove ecosystem along the Sibun River in Belize, which is subject to both changes in sea-level and in the characteristics of the river's drainage basin. Radiocarbon dates from the core show a decreased sedimentation rate from ~ 6 ka to 1 cal ka BP and a marked change in lithology from primarily mangrove peat to fluvial-derived material at ~ 2.5 cal ka BP. Changes in the sedimentation rates observed in mangrove ecosystems offshore have previously been attributed to changes in relative sea-level and the rate of sea-level rise. Pollen analyses show a decreased abundance of Rhizophora (red mangrove) pollen and an increased abundance of Avicennia (black mangrove) pollen and non-mangrove pollen coeval with the decreased sedimentation rates. Elemental ratios ([N:C]_a) and stable isotope analyses (δ¹⁵N and δ¹³C) show that changes in the composition of the organic material are also coeval with the change in lithology. The decrease in sedimentation rate at the site of core SR-63 and at offshore sites supports the idea that regional changes in hydrology occurred during the Holocene in Belize, influencing both mainland and offshore mangrove ecosystems.  相似文献   

Fresip: A mission to determine the character and frequency of extra-solar planets around solar-like stars     

W. J. Borucki  E. W. Dunham  D. G. Koch  W. D. Cochran  J. D. Rose  D. K. Cullers  A. Granados  J. M. Jenkins 《Astrophysics and Space Science》1996,241(1):111-134

FRESIP (FRequency of Earth-Sized Inner Planets) is a mission designed to detect and characterize Earth-sizes planets around solar-like stars. The sizes of the planets are determined from the decrease in light from a star that occurs during planetary transits, while the orbital period is determined from the repeatability of the transits. Measurements of these parameters can be compared to theories that predict the spacing of planets, their distribution of size with orbital distance, and the variation of these quantities with stellar type and multiplicity. Because thousands of stars must be continually monitored to detect the transits, much information on the stars can be obtained on their rotation rates and activity cycles. Observations of p-mode oscillations also provide information on their age and composition. These goals are accomplished by continuously and simultaneously monitoring 500 solar-like stars for evidence of brightness changes caused by Earth-sized or larger planetary transits. To obtain the high precision needed to find planets as small as the Earth and Venus around solar-like stars, a wide field of view Schmidt telescope with an array of CCD detectors at its focal plane must be located outside of the Earth's at mosphere. SMM (Solar Maximum Mission) observations of the low-level variability of the Sun (1:100,000) on the time scales of a transit (4 to 16 hours), and our laboratory measurements of the photometric precision of charge-coupled devices (1:100,000) show that the detection of planets as small as the Earth is practical. The probability for detecting transits is quite favorable for planets in inner orbits. If other planetary systems are similar to our own, then approximately 1% of those systems will show transits resulting in the discovery of 50 planetary systems in or near the habitable zone of solar-like stars.  相似文献   

Book review     

Richard Barakat  Petr Vanicek  Randall L. Mackie  Jacek A. Majorowicz  Ley Truskinovsky  Andrea Borgia  Steven Carey  Ursula B. Marvin 《Pure and Applied Geophysics》1990,134(3):485-507

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Tunnel stability analysis during construction using a neuro‐fuzzy system     

Jos Luis Rangel  Ursula Iturrarn‐Viveros  A. Gustavo Ayala  Francisco Cervantes 《国际地质力学数值与分析法杂志》2005,29(15):1433-1456

This paper presents an alternative strategy to evaluate the stability of tunnels during the design and construction stages based on a hybrid system, composed by neural, neuro‐fuzzy and analytical solutions. A prototype of this system is designed using a database formed by 261 cases, 45 real and the rest synthetic. This system is capable of reproducing the displacements induced at the periphery of the tunnel before and after support installation. The stability of the excavation process is evaluated using a criterion that considers dimensionless parameters based on the shear strength of the media, the induced deformation level in the ground, the plastic radii and the advance of excavation without support. The efficiency and validity of the prototype is verified with two examples of actual tunnels, one included in the database used to train the system and the other not included. The results of both examples show a better approximation than other commonly used techniques. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Domenico Troili (1766): “The true cause of the fall of a stone in Albereto is a subterranean explosion that hurled the stone skyward”     

Ursula B. Marvin  Mario L. Cosmo 《Meteoritics & planetary science》2002,37(12):1857-1864

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AN UNPUBLISHED MEMOIR ON METEORITES BY LYMAN SPALDING, 1810     

Ursula B. Marvin 《Meteoritics & planetary science》1979,14(2):197-205

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Basalts from Mare Crisium     

Graham Ryder  Harry Y. Mcsween Jr.  Ursula B. Marvin 《Earth, Moon, and Planets》1977,17(3):263-287

The stratified core sample returned from Mare Crisium by the Luna 24 unmanned space probe is composed primarily of a new variety of subophitic to ophitic basalt with very low contents of TiO₂ and MgO. This consists of clinopyroxene, calcic plagioclase, olivine, and minor amounts of silica, chromite, ulvöspinel, ilmenite, troilite, apatite, and Fe-metal. Granular metabasalts have the same bulk composition, but mineral phases exhibit less compositional variation. Fine-grained impact melts have similar compositions and are apparently derived from these basalts. We conclude that the basalts, which are chemically distinct from the very-low-titanium basalts found elsewhere on the Moon, represent the local surface flows of Mare Crisium.Sparse fragments of an olivine vitrophyre that is low in TiO₂ but high in MgO and approaches the composition of the Apollo 15 green glasses may be derived from patches of dark mantling materials 20 km from the landing site.Now at Department of Geology, University of California at Davis, Davis, Calif., U.S.A.Now at Department of Geological Sciences, The University of Tennessee, Knoxville, Tenn., U.S.A.  相似文献